Learning curve for Doppler assessment of ductus venosus flow at 11 + 0 to 13 + 6 weeks' gestation.

OBJECTIVE

To determine the number of scans necessary for training sonographers to examine accurately the ductus venosus at 11 + 0 to 13 + 6 weeks' gestation.

METHODS

Ten sonographers with prior extensive experience in the measurement of nuchal translucency thickness were given practical training in the accurate assessment of the ductus venosus. They were then asked to examine the ductus venosus during the routine 11 + 0 to 13 + 6 weeks' scan. Each scan was assessed by an experienced sonographer and classified as being successful or unsuccessful (failure to obtain a waveform, poor quality image with contamination or wrong classification of the A-wave). Each sonographer performed a total of 300 examinations, the data were analyzed in 15 groups of 20 examinations and in each group the percentage of unsuccessful examinations was calculated.

RESULTS

In the total 3000 cases examined by the 10 sonographers there were 2849 (95.0%) successful examinations and 151 unsuccessful, including 104 failures to obtain a waveform, 30 cases where the quality of the image was considered to be inadequate and 17 cases in which the classification of the A-wave was wrong. The overall frequency of unsuccessful examinations decreased significantly with the number of scans carried out (r = 0.982, P < 0.0001). The sonographers required an average of 80 examinations before they could successfully examine the ductus in at least 19 of a group of 20 scans. Although one of the 10 trainees achieved this standard within the first block of 20 scans some of the sonographers required training in 100 cases.

CONCLUSION

Competence in Doppler assessment of the ductus venosus is achieved only after extensive supervised training.